Computational Thermodynamics and Kinetics: High Entropy Alloys/Alloying
Sponsored by: TMS Functional Materials Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Chemistry and Physics of Materials Committee
Program Organizers: Vahid Attari, Texas A&M University; Sara Kadkhodaei, University of Illinois Chicago; Eva Zarkadoula, Oak Ridge National Laboratory; Damien Tourret, IMDEA Materials Institute; James Morris, Ames Laboratory

Monday 2:00 PM
February 28, 2022
Room: 255C
Location: Anaheim Convention Center

Session Chair: Damien Tourret, IMDEA Materials Institute; Vahid Attari, Texas A&M University

2:00 PM  Invited
Using Ab Initio Thermodynamic Modeling to Understand Phase Stability in High Entropy Alloys and How Order-disorder Transition Affects the Performance of Photovoltaic Materials: Geoffroy Hautier1; 1Dartmouth
     First principles or ab initio techniques provide direct access to the energetics of competing phases. I will illustrate the use of these techniques in two different context: high entropy alloys and photovoltaic materials. I will focus first on our recent work on the understanding of phase stability in high entropy alloys pointing out at the inherent reasons for the existence of multicomponent single phase random solid solutions in certain chemistries.[1] In the second part of the talk, I will show how more advanced techniques based on cluster expansion can be used to model order disorder effects in an important photovoltaic materials: Cu2ZnSnS4 (CZTS), and provide insight into the mechanisms limiting solar cell efficiency.[2] [1] G. Bokas, W. Chen, A. Hilhorst, P. Jacques, S. Gorsse, G. Hautier, Scripta Materialia, 202, 114000 (2021)[2] W. Chen, D. Dahliah, G.-M. Rignanese, G. Hautier, Energy & Environmental Science, 14, 3567-3578 (2021)

2:30 PM  Cancelled
Refractory-HEAs: From CALPHAD to Alloy Optimization: Aurelien Perron1; Joel Berry1; Brandon Bocklund1; Richard Otis2; Alexander Landa1; Charles Tong1; Amit Samanta1; Hunter Henderson1; Zachary Sims1; Thomas Voisin1; Vincenzo Lordi1; Scott McCall1; Joseph McKeown1; 1Lawrence Livermore National Laboratory; 2Jet Propulsion Laboratory, California Institute of Technology
    Refractory high-entropy alloys (RHEAs)–encompassing refractory multi-principal element and complex concentrated alloys–are gaining attention as structural materials due to their promising high-temperature properties. However, the fundamental understanding of the complex behavior of RHEAs remains unclear, leading to inefficient design of new high-performance RHEAs. One criterion to be considered during alloy optimization is the phase stability (solid solutions, long/short-range order, miscibility gap, Laves phases, etc.), since properties stem from microstructure and thus phase composition of the alloy. We will present CALPHAD assessments with uncertainty quantification of binary systems from groups 5-6 elements {V, Nb, Ta, Mo, W} based on literature review and new experimental and ab initio data. Extrapolations to multicomponent systems for RHEAs will be discussed with a focus on bcc miscibility gaps and ordering. Finally, TAOS (The Alloy Optimization Software) will be presented, with RHEA optimization used as a case study.

2:50 PM  Invited
Utilizing Nanoprecipitates to Modulate Phase Transformation, Strength, and Ductility of HEAs: Ying Yang1; Eva Zarkadoula1; Easo George1; 1Oak Ridge National Laboratory
    Solid solution high-entropy alloys (HEAs) with the face-centered cubic (fcc) structure can exhibit extensive tensile ductility and excellent toughness, but their room-temperature strength tends to be low. To increase strength, obstacles to dislocation motion such as precipitates are typically added. However, with few exceptions, they tend to embrittle the materials. Precipitates, in addition to spatially confining dislocations and increasing strength, can also retard phase transformation. In this presentation, we will demonstrate a strategy that utilizes computational thermodynamics and kinetics to control nanoprecipitate characteristics, thereby to independently tune both phenomena. The precipitates, by synergistically modulating the strength and transformation of the HEA matrix, produce alloys with improved strength and ductility. We will also discuss molecular dynamics simulation results to show how individual variables such as precipitate size, spacing, volume fraction, and/or the chemical driving force of matrix phase transformation can affect deformation mechanisms.

3:20 PM  
NOW ON-DEMAND ONLY - Predicting Phase Behavior in High Entropy and Chemically Complex Alloys: James Morris1; Louis Santodonato2; Andreas Kulovits3; German Samolyuk4; 1Ames Laboratory; 2Santo Science; 3Arconic Inc.; 4Oak Ridge National Laboratory
    We discuss the ability to rapidly predict phase behavior of high entropy alloys and related compounds without utilizing (or fitting) experimental data. Of particular interest are heuristic approaches that provide prediction of single-phase compositions, approaches that tackle the thermodynamics from a more fundamental point of view, and simulation approaches that provide further insight. We review our own predictive framework for predicting single-phase materials, in the light of significantly increased experimental data, and in comparison with other approaches. We also discuss how chemical disorder can play a critical, non-entropic role in determining phase stability in refractory alloys.

3:40 PM Break

4:00 PM  
Strain and Chemical Interactions in the Early Stages of Precipitation of Multi-component Mg Alloys: Du Cheng1; Kang Wang1; Bi-Cheng Zhou1; 1University of Virginia
    It has been established that chemical and strain interactions dominate the energetics during nucleation of precipitates in solid-state matrix. However, the role of long-ranged strain energy is often overlooked in the first-principles modeling due to the requirement of very large supercells. Here we leveraged the mixed-space cluster expansion (MSCE), in which short and long-ranged interactions are modeled separately in real and reciprocal space, thus overcoming such limitation. In the current work, the coherency strain energy arising from the size-mismatch between alloy constituents is formulated for multi-component alloys, and MSCE approach for binary alloys is generalized to multi-component alloys with arbitrary lattices. The MSCE and Monte Carlo with strain contributions are applied to Mg-Zn-Ca alloys to analyze the structure, stability, and morphology of precipitates at ground state and elevated temperatures. The current work promises a first-principles tool to tune the strain and chemical interactions in multi-component alloys to optimize the precipitation